1. Field of the Invention
The invention relates to a device for enriching a carrier gas or a mixture of carrier gases with the vapour or the vapours of a sparingly volatile substance or a mixture of substances which is present in the form of small solid particles, consisting of a container which comprises a removable, tightly fitting metal body in which in at least one outer wall of the metal body a coiled groove is provided and said outer wall is in contact with the inner wall of the container in such a manner that the groove forms a heatable inner space for receiving the material or the mixture of material, which body is provided with an inlet duct for the carrier gas and an outlet duct for the enriched carrier gas, the ducts opening into the inner space in such a manner that the carrier gas during operation of the device flows through the material or the mixture of materials.
2. Description of the Related Art
Such a device in which the groove is coiled, for example, in the form of a spiral or in a zig-zag or meander-like manner, is known from Pat. No. DE OS 3 339 625. This device, sometimes termed saturator, serves for the adjustment of a defined gas flow or mass flow of sparingly volatile materials which are used, for example, as starting compounds for a chemical deposition from the gaseous phase (CVD method). As examples for such materials are mentioned compounds of IIIB metals in particular or rare earth metals and thorium, in particular metalorganic compounds, for example, thorium acetyl acetonate and thorium trifluoroacetyl acetonate. The saturator which comprises the sparingly volatile material or the mixture of sparingly volatile materials in powder form shows a long flow path and after use can easily be cleaned and be used again. The loaded carrier gas flow emanates from the saturator in the mixing chamber and then enters into a reactor in which the chemical deposition from the gaseous phase takes place.
The disadvantage of the known saturator is that the individual turns of the groove are not closely separated from each other when at the supporting points at which the outer wall of the metal body and the inner wall of the container are in contact with each other layers of powder residues are present so that transverse flow and shortcuts of the carrier gas flow, respectively, may occur which reduce the efficiency of the saturator. A further transverse leak for the carrier gas may occur by the fitting of the metal body, for example a copper block, in the container when the metal body is not densely packed.
Moreover, the known saturator already shows a strong decrease of its efficiency and of the mass flow of sparingly volatile material when the quantity of material present for evaporation and for transport to the CVD reactor is still available. This is due to the fact that the layer of powder in the grooves is slowly exhausted when the consumption increases, collapses, and the carrier gas flows over the surface of the layer without a sufficient saturation being achieved in particular when the provided material has a very low coefficient of evaporation. Moreover in some metalorganic compounds phase transitions occur when the temperature increases which are associated with changes of the density.